In archery, knowing the distance between the archer and the target is very important for shooting with accuracy. Since the path of an arrow is always curved upwardly for taking the gravity into account according to the laws of ballistics, the farther the target, the greater is the initial angle the arrow defines with the horizontal. Therefore, since the initial angle of the arrow is proportional to the range, the archer has to know or somehow evaluate the range in order to set the bow at the right angle before releasing the arrow. An error in the range evaluation may result in missing the center of the target or worse, hit non vital tissues and wound an animal when bow hunting.
For resolving this problem, one can use various instruments for finding the range between the target and the archer. Among the instruments for finding the range, a very effective one is the split image rangefinder which relies on an optical mechanism generating an image having two halves, which are generally a right and a left half. The user then changes the setting of the rangefinder until the two parts of the image appear to be aligned with each other. At that moment, the user can read the distance on the instrument scale and aim accordingly. However, when bow hunting, the archer may not have enough time to find the range, put the instrument away, take the bow, draw, aim and shoot if the prey is in movement or stopped for only a very short period of time. Moreover, the various movements of the archer may be sensed by the prey and alert it.